Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $55.34   13.252%   $62.6737   $62.67   $62.65   $62.70  
  Purchase #2 $249.78   11.495%   $278.4922   $278.49   $278.50   $278.50  
  Purchase #3 $163.36   9.261%   $178.4888   $178.49   $178.50   $178.50  
  Purchase #4 $98.34   3.596%   $101.8763   $101.88   $101.90   $101.90  
  Purchase #5 $206.27   13.390%   $233.8896   $233.89   $233.90   $233.90  
  Purchase #6 $34.90   12.496%   $39.2611   $39.26   $39.25   $39.30  
  Purchase #7 $136.69   4.662%   $143.0625   $143.06   $143.05   $143.10  
  7 purchase totals = $944.68       $1,037.7442   $1,037.74   $1,037.75   $1,037.90